Excellent question! When you upload a PNG (Portable Network Graphics) file, similar colors in your image are combined. This technique is called "quantization". By reducing the number of colors, 24-bit PNG files can be converted to much smaller 8-bit indexed color images. All unnecessary metadata is stripped too.

You need to be confident that the quality of the results you are getting have not been compromised for the sake of getting the smallest possible file size. While it is possible to reduce any image to a tiny fraction of its original size, that approach often leads to a serious amount of visual degradation.

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The EWWW Image Optimizer is a WordPress plugin that will automatically optimize your images as you upload them to your blog. It can optimize the images that you have already uploaded, convert your images automatically to the file format that will produce the smallest image size (make sure you read the WARNINGS), and optionally apply lossy reductions for PNG and JPG images.

ShortPixel makes your website load faster by reducing the size of your images and helps you rank better in Google search. With both lossy and lossless image compression available for all common image types (PNG, JPG, GIF), plus PDF files. The plugin is free to use for 100 images/month.

Introduction Hammy takes your regular content images (only within posts and pages, not custom post types) and regenerates a number of smaller sized images. When a person visits your website, it then automatically provides them with the most appropriate image (or the smallest one possible). This makes for a better experience, especially on mobile.